Sound recording



Sept. 27, 1938. B. F. MltLER SOUND RECORDING Filed July 5, 1935 2 Sheets-Sheet l FIE 2 4 Fumumuumnunnmw INVENTOR BUQTON F M11. LEI? BY PEA m1? ATTORNEY Sept. 27, 1938. B F. MILLER SOUND RECORDING 2 Sheets-Sheet 2 Filed July 5, 1955 PIE. 5.

a B F INVENTOR. Bum-0N F M/LLEP A TTORN Patented Sept. 27, 1938 UNITED STATES PATENT OFFICE SOUND RECORDING Burton F. Miller, Hollywood, Calif., assignor to United Research Corporation, Long Island City, N. Y., a corporation of Delaware Application July 5, 1935, Serial No. 29,931

2 Claims. (01. 179-1003) This invention relates to sound translating detaken along the line II of Fig. 2 and diagramvices and particularly to improvements in light matically showing the arrangement of an optical valves for use in recording sound by the variasystem associated therewith.

ble area method upon a photographic medium. Fig. 2 is a sectional view taken along the line The invention is particularly adapted to be 22 of Fig. 1. 5 used in recording sounds to be later reproduced Fig. 3 is a longitudinal section taken along the in synchronism with motion pictures. line 3-3 of Fig. 2.

In this type of light valve a narrow slit having Fig. 4 is an enlarged fragmentary view of the a width in the order of about one-half mil is light slit and its associated vibrating conductor. provided through which a beam of light is pro- Fig. 5 shows the length of film having a varia- 10 jected onto the sensitized surface of a unible area sound track thereon, as produced by formly moving film. A vibratory current carrythe light valve.

ing conductor is placed in an angular position Fig. 6 is a schematic view showing the applicaover the slit so as to allow about one-half of the tion of a noise reduction circuit. length of the slit to be exposed to the beam of Figs. 7 and 8 are diagrammatic views showing 15 light when no current is flowing through the the method of adjusting the biasing of the conductor. A strong magnetic field having its vibratile conductor.

flux at right angles to the plane of the conductor Fig. 9 is an enlarged fragmentary view of a is provided by a magnetic frame having its poles positive film having a variable area sound track placed closely adjacent the slit and conductor. resulting from the use of the noise reduction cir- 20 When an alternating speech current is passed cuit shown in Fig. 6. through the conductor the interaction between Fig. l is an nlarg d fra men a y v w h wthe magnetic field and the magnetic force proing a sound track p du d y the noise reducduced by the current flowing through the contion circuit in Fig. 6.

ductor causes the conductor to vibrate back and Referring now to Fig. 1, an exciter lamp I of 25 forth in accordance with the amplitude and freconstant intensity projects a beam of light 2 quency of the current thus changing the length of through a pair of condenser lenses 3. from the exposed portion of the slit to the beam of whence it is focused to a point F within the light light. valve generally indicated at 4. Here the beam of In my o e-pending application Serial No. light 2 is changed into a narrow slit of light 30 28,109, filed June 24, 1935, for Sound recordof varying length. An objective lens 5 focuses ing, I have disclosed and claimed a light valve the slit of light upon the sensitized surface of having a single electrical conductor vibratile at a continuously moving film 6. the frequencies to be recorded which is placed Referring now to Figs. 1, 2, and 3, the light across an aperture for producing a noiseless valve 4 comprises a magnetic frame made up of 35 sound track of the double hump type. While it a base plate I of magnetic material, which is secontains claims generic to the arrangement discured at its outer ends to the depending legs 3 closed in detail here, that case specifically disand 9 of an upper magnetic frame Ill by means closes the use of a triangular aperture in the of screws II. The upper frame I 0 has a hollow path of the recording light beam, the single concore I2 provided thereon, which acts as one pole 40 ductor moving parallel to the base of the triof the magnet. A magnetic coil l3 receives a angular aperture. substantially constant direct current to produce An object of the present invention is to adapt a magnetic fiux between the core l2 and a pole the apparatus of my co-pending application repiece !4, which is secured to the lower base plate ferred to above to the recording of a noiseless l in alignment with the core l2, as shown in Fig. sound track of the single hump type. 1. The pole piece i6 is provided with an a er- This is accomplished by modulating the recordture l5 to allow the beam of light to be proing light beam by means of a single conductor jected therethro-ugh. The ends of the core If! moving angularly with respect to a rectangular and the pole piece M are placed closely adjacent slit, each other so as to produce as strong a magnetic 50 The invention further relates to improvements ux as P 8 13 8- in the mounting for the single string conductor. Mounted on the base plate 1 adjacent the pole This invention is illustrated in the accompanypiece M are a pair of bridges I6 and H, having ing drawings in which: raised portions 18 and I9, upon which a vibrating Fig. 1 is a transverse section of a light valve conductor 20 rests. The bridges l6 and I! are 55 formed of insulating material such as Bakelite or hard rubber. The conductor 20 is secured. at one end to a Windlass 2|, for the purpose of adjusting the tension of the conductor 20. The other end of conductor 20 is passed around a spring pressed arm 23 and is secured to a Windlass 25 similar to that of 2!. The arm 23 is pivotable about a stud 24 and is urged outwardly toward the leg 8 by a torsion spring ti thus serving to prevent undue tension from being placed upon the conductor 20. The windlasses 2i and 25 are electrically connected by means of conductors 46 and 41 to terminals 22 and 35 which, in turn, are connected through wires 56 and 5'! to suitable sound recording amplifiers not shown. When a current is passed through the coductor 20, the interaction between the magnetic field set up by the conductor 2i] and the magnetic field between the hollow core l2 and the pole pieces l4 and I5 will cause a movement of the conductor 20 to one side or the other depending on the direction of the current.

Referring now to Fig. 1, the beam of light 2 is focused upon a slit 34 defined by a pair of slit forming members 26 and 2'! which are secured upon supporting members 28 and 29 by means of clamping plates 39 and 3!. The sides of the members and 2'! are engaged by a pair of transversely extending plates l8 and 49, also secured by means of the clamping plates 3% and Si to define the ends of the slit 3G. Of course, it should be understood that the slit 34 may also defined by the edges of the pole piece 14. The members 22 and 29 are secured to the base plate I by means of screws such as 32 and 33.

Referring now to Fig. 4, the vibrating conductor 29 is so adjusted with respect to the slit 34 formed by the members 26 and 2'! that it crosses it at a slight angle, which in the present instance is slightly over one degree. Due to the fact that the natural period of vibration should preferably be above the range of audibility, it is necessary to keep the mass of the conductor 20 as small as possible. In this instance the conductor 263 is in the form of a fiat ribbon about .0005" thick and about .006" wide and is constructed of Duralumin or other light material. These dimensions of course may be varied in accordance with different conditions and requirements. When no current is flowing, the conductor 29 covers approximately onehalf of the area of the slit 34. When an alternating current is passed through the terminals 22 and 35, the conductor 26 is caused to move in a direction perpendicular to the magnetic flux between the hollow core l2 and the pole piece M so as to change the length of the exposed portion of the slit M. The tension and angle of the conductor 2E5 is so adjusted that at full modulation the entire slit 34 is covered at one instant while at another instant the whole area of the slit is exposed. This exposure of the slit 34 is, of course, directly proportional to the amplitude of the current passing through the conductor.

In order to provide adjustment of the conductor 26 in relation to the slit 3d, the bridges l5 and l? have adjusting jaws 36, 37, 3S and 39 thereon. These jaws are preferably formed of a spring material and are secured at their rear ends to the bridges l6 and I! by screws 40 and M. The forward ends of the jaws are bent inward to engage the sides of the conductor 20 and are adjustably secured to the bridges l6 and I! by means of adjusting screws 42 and 43. Thus, both the angle made between the conductor 20 and the slit 34 and also the initial position of the conductor 20 at no modulation may be varied.

At Fig. 5 is shown a section of a positive print of a moving picture film 44, having a variable area sound track portion 45 at one edge thereof formed by the passage of the film before the light valve 4,

Referring to Figs. 6, 7, and 8, I will now describe the application of noise reduction to the recording of sound by my improved light valve. The recording circuit (Fig. 6) comprises a microphone EG wherein sound waves are received and are translated into electrical currents of equivalent wave form and proportionate amplitude. In circuit with the microphone 5B is an amplifier 5| and a transformer 52 which supplies an amplified audio frequency current to the vibrating conductor 26 of the light valve 4. A noise reduction amplifier 53 and rectifier 54 are shunted across the light valve circuit to provide a bias neutralizing current through the conductor 20. Biasing current is provided by a battery 6i so as to hold the conductor 29 in the position shown by the dot and dash lines 29 of Fig. 4 when. no or little sound is being recorded. Thus the center of modulation as represented by the line 58 (Fig. 9) is held to the left of the center of the sound track 59 when recording low level sounds as at point L. When high level sounds are recorded, a current which increases in proportion to the increase in level of the sound is impressed upon the amplifier 53 and rectifier 54. The rectified current is fed to the conductor iii in a direction opposite to that fed by the battery iii to thus neutralize the biasing current produced by the battery 6i. This neutralizing of the biasing current causes the center of modulation of the conductor 2E1 to take a position shown by the full lines of Fig. 4. Thus the center of modulations for high level sounds as shown at point H (Fig. 9) is shifted toward the center of the sound track 59.

The amount of biasing of the conductor is generally dependent upon the kind of sound being recorded. When recording dialogue or music in which the volume is low, or where the change in volume is gradual, the main biasing position of the conductor may be brought nearer to its closing position than in the case of recording staccato sounds such as are produced by a piano or harp. In recording the latter type of sound, more leeway has to be given to the conductor to prevent the high level wave forms from being clipped. This change in biasing position of the conductor is accomplished by means of variable resistance 63 (Fig. 6) and may be effected during recording whenever the tempo of the sound is changed. The change may be made between different types of recordings when the recorder is stopped or during operation of the recorder when the operator is aware of the nature of the sound to be recorded before impression thereof.

The amount of biasing is generally determined by the amount of margin betwen a depression of a wave form and the edge of the sound track as indicated at M (Fig. 8). Referring to Figs. 7 and 8, the margin may also be determined by the dis tance from the left hand edge 65 of the light slit 34 to the position of the conductor 20 at the upper limit of its excursions as indicated by the dotted line 55. In setting the biasing position of the conductor 2%, the variable resistance 63 is manipulated until the distance X, representing one-half of the amplitude of the conductor excursions at an arbitrary low level single frequency .of the distance D (between the zero line of modulation in the biasing position and the edge of the sound track) this percentage, of course, depending on the type of sound being recorded. In recording soft sounds, the distance X may be allowed to cover as much as of the distance D.

In the example shown in Fig. 8, the variable resistance 63 is set so that X will equal one-half D when the conductor is in its biased position. Thus, the margin for low level sounds is indicated by the dimension M. When the amplitude of the sounds is increased to a point at which X exceeds one-half D the change in biasing current causes the mean position of the conductor 20 to be moved downward so as to maintain approximately the same average ratio of X to D. This ratio will remain approximately constant until the conductor 20 reaches its unbiased position as shown by the dotted lines 20'. In this position the ratio of M1 to D1 is still approximately equal to the ratio of M to D. As higher amplitudes are recorded, the zero line of modulation remains at C, provision being made in the rectifier R to prevent a shift of the zero line to the right of C, while the margin again becomes smaller as at Mh to accommodate the higher amplitudes.

Referring to Fig. 9, the zero line of modulation is indicated by the center line 58. Where no sound is recorded on the film only a narrow path of transparency 61 traverses the sound track. As modulations are recorded and increased, the zero line of modulation is moved outwardly toward the center of the sound track until the conductor reaches its unbiased position as indicated by the point H.

Due to the fact that the edges of the sound track are formed by the acute angle between the conductor 20 and the light slit 34, these edges will not form sharp lines but will gradually pass from clear transparency to opacity as shown in Fig. 10. The amount of distortion, however, produced by this shaded zone 68 is negligible due to the fact that its dimension as measured transversely of the direction of the film travel remains constant and thus it is unable in itself to materially effect a varying change of light passing therethrough; it being understood, of course, that the reproduction of sound is dependent upon a change in the amount of light passing through the slit above the lowest audible frequency. The only possible effect of the shaded zone caused by frequency variations in the sound being recorded is to vary the direct current component, which does not change the frequencies making up the sound wave.

The biasing of the conductor 20 may also be accomplished by applying the rectified current from the rectifier 54, which varies in accordance with the amplitude of the sounds being recorded, in a positive sense to the conductor 20. In this case, the normal position of the conductor 20 would be mechanically adjusted so that at low level modulation it would be to the left of the center of the sound track or in a position shown by the full lines 20 of the conductor Fig. 7. With the increase in amplitude of the sound being recorded, the corresponding increase in rectified current from the rectifier 54 would shift the center of modulation of the conductor 20 to the position shown by the dotted lines 20'. That is, instead of variably neutralizing a fixed electrical bias, the fixed electrical bias is eliminated and the rectified current variably biases the conductor in accordance with the average amplitude of the sound waves being recorded.

Having thus described the invention what is claimed as new and desired to secure by Letters Patent is:

1. A device for recording sound waves which comprises a system for transmitting light from a source to a photographic film, means for varying the amount of transmitted light comprising a member arranged in a magnetic field and having an elongated slit therein, a single electrical conductor arranged in the same magnetic field as said member and adjacent the slit in said member to define a light transmitting slot, means for supplying electrical current to said conductor to eflect variation in the space relation between said conductor and said slit in accordance with the instantaneous values of said currents, and means for supplying a current to said conductor to effect a variation in the spaced relation of said conductor with respect to said slit in accordance with the envelope of said electrical currents, said conductor and said slit being disposed in oblique relation to each other.

2. In combination, a member located in a magnetic field and having a fixed elongated aperture therein, the same movable element suspended in a magnetic field and disposed in oblique relation to the aperture in said member, means to supply modulated electrical currents to said movable element to effect movement thereof in front of said aperture in said member in accordance with the instantaneous values of said currents, and means to supply current to said movable element to effect movement thereof in front of said aperture in said member in accordance with the envelope of said electrical currents.

BURTON F. MILLER.

CERTIFICATE OF CORRECTION.

Patent No. 2,151,295. September 27, 958.

BURTON F. MILLER.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 5, second column, line k5, claim 2, for the words "the same" read a; line k6, same claim, for "a" read the same; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 21st day of March, A. D. 1959.

Henry Van Arsdale.

(Seal) Acting Commissioner of Patents.

CERTIFICATE OF CORRECTION.

Patent No. 2,151,295. September 27. 958.

' BURTON F. MILLER.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 5 second column, line 1L5, claim 2, for the words "the same" road a; line l same claim, for "a" read the same; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 21st day of March, A. D. 1939.

Henry Van Arsdale.

(Seal) Acting Comissioner of Patents. 

